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250 ANTIMONY AND ITS ALLOYS
5. Determination of the Arsenic.—See Copper.
Hard lead contains variable quantities of antimony (usually 10-25%)
and may contain small amounts of copper, tin, iron, nickel, arsenic, etc.
The following table contains the results of analysis of samples of hard lead
obtained directly, from ores of lead and antimony (Schnabel) :
Composition of Hard Leads
OberharzJlI . . [ill. . . Freiberg .
81-71 . i 82-44 . : 82-08
17-69 16-90 i7'34 15
0-62 0-68 0-62
ANTIMONY AND ITS ALLOYS
Owing to its brittleness, antimony is rarely used as such, but it forms
part of many industrial alloys, such as white bearing metals, type metal, etc.
Methods for determining the impurities commonly accompanying com-
mercial antimony are therefore described, since the value depends on the
Lead-antimony alloys are treated under lead, while alloys of antimony
with tin alone or with tin and lead together (white metals) arc dealt with
along with tin.
Analysis of commercial antimony is generally limited to the determina-
tion of its commoner impurities : lead, bismuth, copper, iron, arsenic and
10 grams of the finely powdered sample are treated with aqua regia
(140 c.c. HC1, 20 c.c. HN03) diluted with an equal volume of water, the
solution thus obtained being treated with 60-70 c.c. of 50% tartaric acid
solution, then made alkaline with concentrated sodium hydroxide solution
and subjected to a current of hydrogen sulphide. The separation of the
sulphides is facilitated by heating on a water-bath, the precipitate being
filtered off and washed once or twice with hot water containing a few drops
of sodium sulphide. The precipitate is then dissolved in a little hydro-
chloric acid containing bromine and 1-2 drops of tartaric acid added to
the solution, which is rendered alkaline with sodium hydroxide and again
precipitated with hydrogen sulphide to ensure the complete elimination
of the antimony. After a short rest on the water-bath, the liquid is filteredtic Determination of Tin in Ordinary Bronzes).